The present invention relates generally to illumination and image acquisition systems and particularly to a color flash image acquisition assembly that is suitable for electrical circuit inspection, including the inspection of in-fabrication flat panel displays.
Automated optical inspection (AOI) systems are typically employed in the inspection of electrical circuits, including printed circuit boards, flat panel displays, chip carriers, integrated circuits and the like. Commercially available AOI systems include the Inspire(trademark) 9060, SK-75(trademark) and V-300(trademark) systems for inspecting bare printed circuit boards, the Trion(trademark) system for inspecting populated printed circuit boards, FPI-6090(trademark) and FPI-7590(trademark) systems for inspecting flat display panels, and ICP 8060(trademark) system for inspecting chip carriers. All of the above systems are commercially available from Orbotech Ltd. of Yavne, Israel.
A system for acquiring color images using color flashes in combination with a black and white camera is described in European Patent Application 1,098,190 A2, to Orbotechxe2x80x94Schuh, GMbH and Co., KG, published on May 9, 2001, the disclosure of which is incorporated herein by reference.
The present invention seeks to provide an improved system for acquiring color images of surfaces. A typical application for images acquired using a system configured and operative in accordance with the invention is for inspecting electrical circuits, particularly flat panel displays, for defects.
In accordance with a general aspect of the invention, an improved system is provided for acquiring color images. The improved system is particularly useful for acquiring brightfield color images of specular surfaces, such as portions of in-fabrication flat panel displays. The invention may be employed wherever it is desired to acquire a brightfield color image in which each of the component images, for example red, green and blue components, are in very precise and accurate alignment.
In accordance with an embodiment of the invention, the improved system comprises a sensor imaging a portion of a generally specular surface, and an illuminator providing at least two spectrally different and temporally separated flashes of light. The sensor and illuminator are arranged such that light from each flash of light output is incident on the portion of the specular surface generally at the same angle of incidence, and such that the sensor images a reflection of light reflected by the portion of the specular surface incident thereon. An image combiner is provided to combine images acquired with illumination from different flashes of light to produce a combined image.
Embodiments of the present invention may include one or more of the features which follow:
The illuminator includes a set of flash lights, and each of the flash lights emits light of a different color.
The set of flash lights comprises two or more flash lights, selected from a red flash light, a green flash light and a blue flash light.
The flash lights emit light within a given spectral range. The spectral ranges of the respective flash lights may be either overlapping or not overlapping.
The flash lights are LED emitters.
The LED emitters emitting red flash light, green flash light and blue flash light are mutually set apart from each other.
The LED emitters emitting red flash light, green flash light and blue flash light are mutually interlaced.
A light homogenizer is disposed between the illuminator and the surface. The light homogenizer treats light emitted by the LED emitters to appear as if emitted by an extended light source.
An at least partially reflective surface is disposed between the illuminator and an illuminated portion. The reflective surface reflects light from the illuminator to impinge on the portion generally along an axis normal thereto.
The reflective surface disposed between illuminator and the illuminated portion is configured as a beam splitter so as to transmit light emitted by the illuminator and reflected by the surface to impinge on the sensor.
The sensor is also disposed along an axis that is normal to the illuminated portion.
The illuminator and the sensor are configured and arranged such that an optical image of the imaged portion is a bright field image.
The generally specular surface being imaged is a surface of an in-fabrication electrical circuit, which is, for example, an in-fabrication display panel.
The system further comprises a defect detector operative to receive a combined image and to detect defects in the substrate in response to analyzing the combined image.
In accordance with another general aspect of the invention, the improved system is employed as part of a process for manufacturing electrical circuit substrates, such as flat panel displays. The process includes: forming a pattern on a generally specular substrate; illuminating a portion of a surface of the substrate with at least two spectrally different and temporally spaced flashes of light, each flash of light being incident on the surface at generally the same angles of incidence; acquiring at least a first optical image of the portion with a camera arranged to receive light from a first flash reflected by the portion of the generally specular surface; acquiring at least a second optical image of the portion with the camera arranged to receive light from a second flash reflected by the portion of the generally specular surface; combining the first optical image and the second optical image to form an inspection image; inspecting the inspection image for defects; and in response to the inspecting, performing a post inspection operation on the substrate. The post inspection operation includes at least one of the following: discarding the substrate, repairing the substrate or confirming that the substrate is not defective.